Hitherto, in cases of dental restoration requiring the esthetics, restoration by dental prostheses such as resin jacket crowns, porcelain jacket crowns, resin facing crowns, and porcelain facing crowns, and restoration by filling with composite resins, have been widely employed. In particular, in recent years, since the resin capacity is greatly improved, restoration by resin facing crowns, or by filling with composite resins, which is easy in operation and inexpensive, is the main current in the restoration.
The resin facing crowns are produced by the operation in which tooth color resins called as composite resins for crown and bridge are applied on the surface of a crown and after forming the surface characterization, are polymerized and hardened. The application with the composite resins for crown and bridge is carried out by application with an opaque resin, application with a dentin resin, and application with an enamel resin, to thereby impart the surface characterization. In this case, the operation is carried out in such manner that primary polymerization (polymerization while retaining unpolymerized portions) is carred out at every stage of the application with an opaque resin, the application of a dentin resin, and the application with an enamel resin, and that when a prescribed surface characterization is completed, the applied resins are completely polymerized. However, since when such composite resins for crown and bridge are once completely polymerized, unpolymerized portions do not remain, the later applied composite resins for crown and bridge do not adhere but peel off and drop from the added portions. For this reason, it is substantially impossible to undergo forming the surface characterization after the resins have been once completely polymerized. When it is forced to undergo forming the surface characterization, an operation in which one layer of the surface of the polymerized and hardened resin is shaven off, and the resulting surface is coated with a radical polymerizable substance containing a polyfunctional (meth)acrylate, such as opaque liquids of composite resins for crown and bridge and dilute solutions of pastes for adjusting the shade, to again apply with a composite resin for crown and bridge, is employed. However, the adhesive strength in the added portions is at most about 60 kgf/cm.sup.2 so that no satisfactory adhesive strength is obtained. In addition, the opaque liquids of composite resins for crown and bridge and the dilute solutions of pastes for adjusting the shade are so viscous that the shade of the photopolymerization initiator remains. Therefore, they can not be satisfied at all for use as an adhesive.
In cases of filling composite resins, the resins are filled in a tooth cavity in a mouth and after forming the surface characterization, are polymerized and hardened to undergo restoration. However, since no adhesive to strongly adhere the filling composite resins to each other is available, after the resins have been once completely polymerized, it is impossible to undergo additional filling for the purpose of forming the surface characterization. For this reason, operations for removing the filling composite resins filled and hardened in the tooth cavity and again undergoing filling were necessary.
Taking into consideration the present state that no adhesive for adhering dental resin composite materials such as composite resins for crown and bridge and filling composite resins to each other is present and that with the opaque liquids of composite resins for crown and bridge and the dilute solutions of pastes for adjusting the shade to be used as a substitute, not only a satisfactory adhesive strength is not obtained, but also the viscosity is high, the color remains, the operability and esthetics are not satisfactory, the present inventors had as their object to developing an exclusive adhesive for dental resin composite materials, which has a proper viscosity, which is free from the color remaining and is superior in the operability and esthetics, has a satisfactory adhesive strength, and which is safety even when it is used in the mouth.